Forceps and tweezers are common tools made in the shape of a stylus in which there is a working end or tip and a part that rests on the fleshy space between the base of the index finger and the thumb. Typically, forceps and tweezers are held like a pencil where the thumb, index finger and middle finger hold forceps or tweezers close to the working end. As used herein and as in human anatomy, the anatomical term proximal is nearer and distal is further away on the extremities in relation to the torso. Similarly, in relation to the hand, typically the part of a forceps or tweezers resting over the portion of the hand between the base of the thumb and index finger is the proximal end, whereas the tips of forceps or tweezers can be referred to as the distal end.
Forceps and tweezers have opposing blades or members and fine tips enabling the hand to pick up and hold parts of various objects with a range of grip intensity. The opposing actions of the thumb and the long fingers manipulate the blades to move the tips of forceps or tweezers together. Opposition, i.e. moving the tip of the thumb and tips of the long fingers closer to each other, is done by contracting opponens muscle of the thumb and the lumbrical muscles of the long fingers. The lumbricals are small muscles located in the palm of the hand and their contraction pulls the proximal interphalangeal (PIP) bones at the base of the long fingers. The opponens muscle of the hand pulls the base of the thumb. When using forceps or tweezers, the function of fine pinch is under control of the opponens muscle and the lumbrical muscles. However, the function of gross pinch is under control of the opponens muscle of the forearm that pulls the distal portion of the thumb, and the deep flexor muscles of the forearm pull the distal portion of the index finger and the distal portion of the middle finger.
Typically, the blades of a forceps or tweezers receive support in the resting hand from the middle finger that crosses underneath them and the portion of the hand between the thumb and index finger. However, when the distal tips of a forceps or tweezers are moved together, the support for the forceps or tweezers in the hand changes and greater support is generated at the tips of the thumb and index fingers to hold the forceps or tweezers. This can cause muscle and joint strain.
Some of the factors that can cause strain in the hand when using a common forceps or tweezers include the width of the blades, the spring force of the blades, the way the hand and wrist joints function when grasping or pinching with a forceps or tweezers, the number of muscle fascicles of a muscle used to contract a corresponding muscle, and the position of the fingers on the forceps or tweezers. Typically, wider blades of a forceps or tweezers are easier to hold than narrow blades, and generally require less muscle tension to pinch. The spring-like properties of the material used for typical forceps or tweezers and the connection of the blades can affect the muscle force required to close a forceps or tweezers.
Most joints flex and extend and have a small degree of side to side motion, while other joints can move in more than one direction. In the latter joints, such as the thumb, there is larger surface contact area at the center of the joint than the periphery of the joint. When the thumb opposes the center of the long finger tips, the bones at the base of the thumb contact more surface area. When the thumb opposes the index finger or small finger, then bone contact in the joint is at the respective sides of the joint, with the joint contact area of the bones being less than when the thumb opposes the long fingers. Therefore, the common forceps or tweezers force the thumb to move to the radial side of the thumb joint where there is less bone contact surface area.
Muscles are made up of sub groups called muscle fascicles. These fascicles are made up of groups of muscle fibers. The amount of muscle fiber contraction determines the strength or the pinch force used to hold an object between the tips of the forceps or tweezers. When the radial side of the thumb joint is used to hold a common forceps or tweezers, the thumb opposes the index finger, and the radial side of the opponens muscle contracts to pull the thumb. In the common forceps or tweezers, fewer muscle fascicles and fibers are typically used for pinch strength when the thumb opposes the index finger than when the thumb opposes the center of the long finger tips. If fewer muscle fascicles and fibers are used to pinch, than potentially available, there is a greater chance of fatigue and strain in these muscles and their fascicles. Therefore, utilizing more muscle fascicles can desirably increase pinch strength and reduce muscle fatigue and stress. Thus a forceps or tweezers that increases the number of muscle fascicles used to pinch a forceps or tweezers is desirable.
Moreover, pinch strength is also affected by the number of muscles used in pinching. When the thumb and index finger pinch, one lumbrical muscle is used to pinch the index finger against the thumb. However, two lumbrical muscles, one for the index finger and one for the middle finger, are used in pinching when the thumb opposes the space between the index finger and middle finger. Pinch forces are potentially greater when the thumb opposes both the index finger and the middle finger than when the thumb opposes the index finger alone. This potential grip strength is greater because more opponens muscle fascicles are available when the thumb opposes the space between the index finger tip and the middle finger tip than when the thumb opposes the index finger tip. Thus, opposing the thumb to the space between the index finger and the middle finger has greater efficiency and can reduce muscle fatigue.
Additionally, hand strain can occur while using a common forceps or tweezers. This is because the thumb and index finger have a natural tendency to advance toward the tip of the common forceps or tweezers when holding a stylus-type tool, creating the potential for excessive squeezing of the forceps or tweezers. This can create exaggerated flexion at the distal interphalangeal joint (DIP) of the thumb and exaggerated index finger flexion at the middle interphalangeal (MIP) joint of the index finger while the DIP joint of the index finger extends. With such exaggerated flexion, the tips of the fingers squeeze and retract proximally, providing feedback or added pressure, i.e. “the feel”, that an object is being supported by the hand. Maintaining this awkward position can also strain finger and wrist joints and ligaments, especially when they suffer pre-existing damage. Such awkward but common position of exaggerated flexion results from the forearm muscles and tendons contrasting the middle phalange of the index finger and distal phalange of the thumb. This typically requires significant force from the forearm muscles, which can add strain and pressure within the carpal tunnel (CT) where the tendons of the superficial flexor forearm muscles transmit direct pressure on the transverse carpal ligament (TCL) and median nerve. Thus, the strain and pressure in the CT from the tendons of the contracted superficial flexor forearm muscles resulting from such awkward position can lead to median nerve irritation and carpal tunnel syndrome (CTS). Furthermore, strain in the muscles in the hand and forearm can cause repetitive strain syndrome of the involved muscles.
A typical problem posed with common forceps and tweezers is that frequent use can cause pain in the hand, wrist and forearm and lead to CTS. This problem has not been solved because the common forceps or tweezers generally adapts a stylus-type tool to pinch small objects. Such stylus-type tools can force the hand into an uncomfortable position with the hand compensating for exaggerated finger flexion, as discussed above, leading to this problem.
Efficiency is reached when the parts of the hand work in harmony to perform a task. The goal of handle design for a forceps or tweezers, as well as an objective of the method and apparatus of the present invention is to promote such efficiency. An efficient handle design should maintain the hand in a comfortable position. A further goal of any handle or grip design, as well as a further objective of the present invention, is to facilitate the function of the hand and forearm muscles so they work in concert. Another goal of handle design, as well as a further objective of the method and apparatus of the present invention, is to facilitate the function of the joints in the hand and wrist to reduce ligament strain.
Furthermore, another goal of handle design for a forceps or tweezers, as well as an objective of the method and apparatus of the present invention, is to promote reduced pinch strength typically required for holding an object. When less pinch strength is required to hold objects, there is less strain to joints and their surrounding ligaments.
Therefore, what is needed is a handle for a forceps or tweezers, and a method and apparatus for designing such a handle for a forceps or tweezers, that fulfills the previously mentioned goals. Such a handle for a forceps or tweezers should promote a reduced incidence of repetitive strain disorder and joint injury.
Forceps and tweezers, such as surgical forceps and tweezers, generally fall into three common types. The first type has two side by side blade members hinged at one end and tips at the other respective end. The blade members move toward each other and the tips come together to grasp and hold. The blade members of this first type of forceps and tweezers can meet and cross and then extend like a scissors. The blade members of the second type of forceps and tweezers are oriented one on top of the other instead of side by side. In the second type, the handles extend perpendicular to the orientation of the blade members and typically the handles have rings to engage the fingers. The blade members in the second type meet the handles at a hinge. Moving the ring handles moves a pivoting member to open or close for grasping or cutting tissue. A third type of forceps and tweezers uses a lever or slide to actuate a mechanism that opens and closes the jaws of an instrument.
Examples of the side-by-side blades of the first type of forceps or tweezers include those in U.S. Pat. Nos. 288,096, 987,095 and 2,540,255, which are fruit pickers. U.S. Pat. No. 5,893,877 illustrates a forceps or tweezers which is a microsurgical cup forceps. U.S. Pat. No. 5,002,561 illustrates a protective hand forceps and U.S. Pat. No. 5,176,696 is related to handles for microsurgical instruments. The handles in U.S. Pat. No. 5,176,696 oppose the thumb to the index finger and middle finger.
Examples of the ring or second type of forceps or tweezers include those illustrated in the following U.S. patents, namely U.S. Pat. No. 4,043,343 illustrates forceps, U.S. Pat. No. 4,674,501 illustrates a surgical instrument, U.S. Pat. No. 5,160,343 illustrates a surgical instrument handle and forceps assembly, U.S. Pat. No. 5,211,655 illustrates multiple use forceps for endoscopy, U.S. Pat. No. 5,234,460 illustrates laparoscopy instrument, and U.S. Pat. No. 5,318,589 illustrates a surgical instrument for endoscopic surgery.
Examples of the lever or third type of forceps or tweezers include those illustrated in the following U.S. Patents, namely U.S. Pat. No. 4,644,651 illustrates an instrument for gripping or cutting, and U.S. Pat. No. 5,470,328 illustrates a surgical instrument handle and actuator means, in which both devices described press down a lever. Other examples of the lever or third type of forceps or tweezers include those illustrated in U.S. Pat. No. 5,147,380 which illustrates a biopsy forceps device having locking means and in U.S. Pat. No. 5,184,625 which illustrates a biopsy forceps device having improved handle, both having sliding locking devices. Another example of the lever or third type of forceps or tweezers is illustrated in U.S. Pat. No. 5,976,121 as a medical manipulator that has a lever that straddles a shaft that has a distal end with a grasping part.
What is needed is a forceps or tweezers allowing the hand to pinch with greater efficiency, improved stability and reduced joint and muscle strain and tension. The problem with many of the above examples of common forceps or tweezers is that their design and operation does not take advantage of the greater pinch strength available from opposing the thumb to the index finger and middle finger instead of opposing the thumb to the index finger. Furthermore, the above styles of handles for common forceps or tweezers do not efficiently utilize the palm of the hand to support the handle. In addition, the handles for common forceps and tweezers do not efficiently utilize the ring finger and small finger to hold and stabilize the handle of the forceps and tweezers.